Presently-known signal apparatus or air horns include a vibrating diaphragm which acts as a valve to introduce pulsations in a fluid stream to cause an air column in the horn to vibrate at a defined frequency which is a function of the shape and dimensions of the horn. For best results, the oscillations of the diaphragm should correspond to the frequency of the horn. In the past, to accomplish this, it has been common to change the diameter of the diaphragm for different horns, so that the diaphragm's natural frequency corresponds to the horn frequency.
However, more recently, it has been found that by the use of complex diaphragm arrangements, including various damping mechanisms disclosed in U.S. Pat. Nos. 2,579,784, 2,789,529 and 3,117,552, that a single diameter diaphragm can be made to operate satisfactorily with a fairly wide range of horn frequencies. Such diaphragm arrangements thereby avoided the need of changing the diaphragm for each horn having a different frequency. In such single diameter diaphragms, the basic frequency of the horn is substantially lower than the natural frequency of the diaphragm, and the diaphragm is forced to vibrate at the frequency of the horn. However, in some cases, the horn has a frequency at the higher end of the range of horn frequencies, and the difference between the horn frequency and the natural frequency of the diaphragm is relatively small. In such cases, there is a tendency for the diaphragm to want to vibrate at its own natural frequency, which is undesirable, since the diaphragm's natural frequency is different from the horn frequency which is desired.
Accordingly, it would therefore be desirable to provide an arrangement which ensures that the diaphragm will vibrate at the horn frequency, and not its own natural frequency. It is also desirable to provide a diaphragm arrangement for such signal apparatus which is simple and inexpensive to construct.
Broadly, it is an object of the present invention to provide an improved signal apparatus which overcomes one or more of the aforesaid problems. Specifically, it is within the contemplation of the present invention to provide an improved signal apparatus which utilizes a single diameter diaphragm for a relatively wide range of horn frequencies, without employing complex diaphragm arrangements.
It is a further object of the present invention to provide an improved signal apparatus which ensures that the diaphragm will vibrate at the desired horn frequency, rather than its own natural frequency, even when the difference between the horn frequency and the diaphragm frequency is relatively small.
It is a still further object of the present invention to provide an improved signal apparatus which employs a diaphragm arrangement of simple construction, which is economical to manufacture and efficient in its operation.